ETS-backed implementation of Mailglass.SuppressionStore (D-28).

Test-speed + narrow production use case (single-node, read-heavy, sub-100-entry lists). Default impl remains Mailglass.SuppressionStore.Ecto — adopters override via:

config :mailglass, :suppression_store, Mailglass.SuppressionStore.ETS

Key shape

ETS keys: {tenant_id, address, scope, stream_or_nil} (mirrors Ecto UNIQUE constraint (tenant_id, address, scope, COALESCE(stream, ''))).

Lookup algorithm

check/2 tries three scopes in order (matching Ecto's OR-union):

1. {tenant_id, address, :address, nil}
2. {tenant_id, domain(address), :domain, nil}
3. {tenant_id, address, :address_stream, stream} (only when stream is set)

First hit wins. Expiry filter at read time (expired entries not returned).

UPSERT behaviour

record/2 with the same {tenant_id, address, scope, stream} key overwrites the existing entry (equivalent to Ecto's on_conflict: {:replace, [...]}).

Test override pattern (RESEARCH §5.3)

Tests scope by unique tenant_id to avoid cross-test interference — no per-pid ownership needed (ETS table is global). Tests that need a clean slate between runs call Mailglass.SuppressionStore.ETS.reset/0.